1. Field of the Invention
This invention relates to a granulating and coating machine and more particularly to a granulating and coating machine which is capable of granulating, coating, mixing, and drying granular and powdery raw materials with high productivity to obtain granulated or coated products having narrowly dispersed particle size and good sphericity.
2. Prior Art
Granulation is one of the most useful ways of processing in many industries. But it has long been one of the most difficult processes. In the traditional methods, which comprises many steps, each unit step requires different unit equipment and skilled workers. For this reason, traditional granulation is very low in productivity, very difficult in technology and does not conform to GMP (Good Manufacturing Practice).
Fluidized bed granulation was developed as a quite new process to overcome the drawbacks of traditional granulation. Specifically, it requires only one piece of equipment, a fluidized bed granulator. It easily conforms to GMP.
Fluidized bed granulation, however, has big disadvantages both in technique and in quality of the product. Fluidization is performed only on the hard balance of lifting force of air and gravity on the particles. The balance easily tends to be upset since the particles' size, shape and weight are changed during fluidization. This is the basic difficulty of fluidized bed granulation. Furthermore, the concentration of particles should be lowered to avoid any interaction between them and keep a good fluidizing state. This makes the space yield of fluidization granulation very low. Qualitywise, enlarged particles obtained by this method are generally very bulky, coarse and brittle, due to the lack of kneading and tumbling and also are distributed widely in their particle size.
In order to overcome these disadvantages, there were provided many developments in fluidized bed granulators not only for granulating but also for coating, mixing, and drying granular and powdery materials for use in the fields of medicine, foods, powdered metals, catalysts, ferrite, ceramics, detergents, cosmetics, dyestuffs, pigments, toner, etc.
Examples of such prior development are German Pat. Nos. 2738485 and 2805397 which disclose machines having a rotary plate or disk over a mesh provided at the bottom of a granulating casing. This prior art can be used for granulation and coating, but it has a drawback in that the granulated materials are caught between the rotary disk and the mesh so as to be disintegrated by being rubbed against the mesh when the rotary disk is rotated. In this prior art, another drawback which should be mentioned is that the powdery materials tend to leak through the mesh. In addition to these drawbacks, this prior art can not control the bulk density of the granulated materials, as the result of this, it is able to granulate only heavy products with widely distributed particle size.
As another prior art, there is provided a machine including an agitator in a casing and a disintegrator arranged along side of and over the agitator. This prior machine can provide relatively high productivity, but ha drawbacks in that the shapes of the granulated or coated products are not uniform, it is difficult to obtain products with good sphericity, and the particle size of the products distributes to the wide range. Mcreover, in this prior machine, as the drying of the products is impossible, other drying equipment is required separately.
Further, Japanese Patent Publication No. 56-35891 discloses a granulator wherein a side slit for feeding gas into the casing from the side thereof is provided in the side wall of the casing in addition to the prior machine disclosed as the second prior art. This prior art, however, has the same drawbacks as the second prior art has, except for the improvement in the drying effect achieved by the gas fed through the side slit.